Method of preparing zein solutions directly from gluten



Patented Sept. 26, 1944 2,359,203

METHOD OF PREPARING ZEIN SOLUTIONS DIRECTLY FROM GLUTEN Roy E. Coleman,Chicago, Ill. assignor to Time, Incorporated, a corporation of New YorkNo Drawing. Original application November 30.

1942, Serial No. 467,402. Divided and this application October 25, 1943,Serial No. 507,597

6 Claims. (Cl. 106-153) This invention relates to methods of preparfor ashort period of time generally not exceeding commercially usablesolutions and coating ing about three hours. It is preferred that thecompositions of prolamines or prolamine-conextraction time be not longerthan about onetaining proteins directly from glutens, either half toabout one hour since within this time corn, wheat, barley, etc. It isparticularly diand at the temperatures stated, the zein in the rected tosuch methods which will produce solugluten is extracted and is notdeleteriously tions and coating compositions of the alcoholaffected.

soluble portion of corn gluten, of controlled solu- The extract solutionobtained as above detion and gelling characteristics. Thisapplicascribed is now separated from the residual gluten tion is adivision of my copending application, 10 by filtration, pressing,centrifugal separation Serial No. 467,402, filed November 30, 1942. orin any other desirable manner and is distilled Heretofore, in thepreparation of zein solu-' or otherwise treated to remove all or some ofthe tions and coating compositions, including the diluent, as desired.It may be filtered prelimsubstantially non-aqueous zein solutions andinarily to the step of removing the diluent, if coating compositions ofcontrolled solution and necessary. The resulting residue is a solutiongelling characteristics as described in my prior of zein orzein-containing protein in the base Patent No. 2,185,110, grantedDecember 26, 1939, solvent alone with all of the diluent from the forexample, the zein is initially isolated from extract solution removed,or in the base solvent corn gluten and then dissolved in suitable solandthat portion of the diluent which has not vents to form the desiredsolutions. To isolate been removed. The residual gluten, which stillzein from corn gluten as a commercially usable contains some protein,may be freed from repowder is a laborious and expensive process,intained solvent by washing and recovered for volving steps ofprecipitation, settling, filtering, further use as a cattle food or forother purwashing and drying. The solubility of the zein poses. in zeinsolvents and the solution characteristics The resulting zein orzein-containing solutions such as stability and gelling tendencies arelargely in accordance with the present invention, over dependent uponthe care exercised in carrying a wide range of concentrations, arestable on out the steps of the process. standing at temperatures of 80F. and below and In accordance with the present invention I do notseparate even when cooled to temperprepare solutions of zein orzein-containing proatures of 50 to 70 F. and somewhat below. teinsdirectly from corn gluten under conditions When cooled even totemperatures as low as 10 that will readily produce a wide variety ofzein above zero or'to zero, solutions prepared in ac" products in so faras properties and solubility cordance with the present invention maysepcharacteristics are concerned, and thereby avoid arate and becomesolid; however, on heating the expense and objections incident to thepreag i to perat of from bout t liminary isolation of zein in powderform. In F., a re-solution is eiiected, either without stircarrying outthe present invention, corn gluten, ring t Slight Stirring, and eSolutions for example, in granular or powdered form, is return to theirnormal form at the re-heating treated with a suitable solvent mixture,without temperatures. In general, these solutions are the establishmentof special conditions of hy- 40 s bst t y elling and have but a slightdrogen ion concentration either in the solvent tendency to increase in.viscosity; that is, to or in the gluten, to extract the zein from thethicken or become heavier in body. In many gluten. The solvent mixturecomprises a base instances they exhibit practically notendency solventhaving a boiling point above about 125 to thicken or to gel overpractical periods of time 0., preferably above about 150 C. and adiluent 45 in the order of about 3 to 6 months and even or extenderhaving a boiling point below about up to one year and longer. Thesesolutions remain 125C. and, preferably. of about C. and below. stableand reasonably constant in their char- The base solvent is itself asolvent for zein'and acteristics during the periods necessary for thediluent may be, and preferably is, also a soltransportation anddistribution, either in bulk vent for zein. The base solvents anddiluents in 50 or in packages, or for storage for reasonable accordancewith the present invention will be periods of time, and hence theirfield of applicadefined fully hereafter. bility is greatly increased.

The extraction is carried out at elevated term In general, in theconcentration of zein or peratures, say from about to about 170 F.,other prolamine in commercially usablesolutions preferably between aboutto about F., 55 containing about 12 to 30% of protein, the

amount of base solvent necessary to obtain these concentrations in thefinal solutions is in and;

of itself iusufficient to give the proper relation between solvent andgluten for efiective extraction results. If large amounts of therelatively high boiling point base solvents are used, sufilcient to givethe proper relation between solvent and gluten, the extraction resultsare not sufiiciently effective and, moreover, the cost of treating theextracts to obtain the desired solids concentration is so prohibitive asto make this procedure commercially unfeasible.

The desired solvent to gluten ratio in accordance with the presentinvention is secured by adding to the desired amount of relatively highboiling point base solvent or mixture of base solvents one or more ofthe so-called relatively low boiling point diluent solvents. To obtaineffective extraction results, the solvent to gluten ratio should be inthe order of about 2 to parts by weight of the former to about 1 part byweight of the latter. Due to the presence of a diluent or extender inthe extracting solvent, the solvent to gluten ratio may be less thanthat which would be required with a base solvent alone and,notwithstanding the lower solvent to gluten ratio, the extractionresults are generally more effective. The diluent solvent or extendermust have a lower boiling point and distillation range than the basesolvent. It is preferred that these diluent solvents or extenders be ofsubstantially lower boiling point and distillation range than the basesolvent, as pointed out above.

Base solvents The base solvents are relatively high boiling compounds ormixtures of compounds as pointed out above and have a suitable balancebetween the hydrocarbon constituents or radicals present in the olventor solvent mixtures and the polar constituents or radicals presenttherein. A. certain proportion of hydroxyl radicals in the base solventsis required to secure solvent action. Other .polar radical such as -O-(ether oxy gen), -Cl, NHz and 0001-1 appear to aid or cooperate with the-OH in securing the necessary conditions of polarity in the basesolvents (in which term I include mixtures of base solvents), forsolvent action.

The proportion of polar radicals to hydrocarbon or non-polar radicalswhich I have found to be desirable lies within a range which extendsbetween the limits of absolute methanol on the one hand, having 53%hydroxyl and 47% hydrocarbon radicals, and absolute ethanol on the otherhand having 37% hydroxyl and 63% hy drocarbon radicals. The benzylradical act as if it were intermediate the methyl and ethyl radicals.This range is approximate and may vary somewhat depending on the solventor sol-- vent mixture used. The limits of this range are indicative ofsolvent properties and provide a close and adequate guide to enable theoperator, by simple experimentation. to determine the re quiredbalanceof polar and hydrocarbon radicals in the base solvent or mixtureof base solvents in accordance with the present invention.

It may be stated that the base solvents in ac cordance with the presentinvention may be any one of the solvents or mixture of solvents de--scribed in my prior Patent No. 2,185,110 which has the require balanceof polar and non-polar radicals, and a boiling point above about 125(3.. preferably, above about 150 C. as pointed out accuses above. For amore complete description 0! the kinds of solvents which may be used asbase solvents in accordance with the present invention than is disclosedherein, reference is made to the description of these solvents in myprior Patent No. 2,185,110.

Examples of base solvents in accordance with i the present invention arethe glycols such as diethylene glycol, propylene glycol, triethyleneglycol and mixtures thereof, including "mixtures which contain ethyleneglycol; diacetone alco hol; closed chain cyclic alcohols such as benzylalcohol, cyclohexanol, furfuryl alcohol, .tetrahydrofurfuryl alcohol andmixtures of closed chain alcohols; glycol ethers such as ethylene glycolmono-methyl ether, diethylene glycol monmmethyl ether, ethylene glycolmono-ethyl ether, diethylene glycol monoethyl and mixtures of glycolethers; mixtures of two or more of the foregoing enumerated basesolvents; mixtures of one or more of the foregoing base solvents withglycerine. or other solvents or mixtures 01 solvents, providing themixture has the required polar to non-polar radical balance and therequired relatively high boiling point. It is to be understood that theforegoing specifically mentioned solvents or mixtures of solvents is notintended to be inclusive of all the base sol vents which may be used inaccordance with the present invention since they are merely set forthfor illustrative purposes.

Diluent solvents The diluent solvents or extenders in accordance withthe present invention may be, suitably, a single solvent or a solventmixture which may 'or may not be a solvent for. zein or other prolamine,as desired. Thus, the extending solvent may be one or more of thewell-known alcoholic zein solvents such as anhydrous methanol, orconstant boiling point mixtures azeotropes) of aliphatic alcohols suchas ethyl alcohol and 91% isopropyl alcohol. For convenience herein Iterm these alcoholic solvents concentrated alcohol solvents. The diluentsolvents may also be one or more of the concentrated alcohol solventscontaining additional amounts of water, say from 40% to 50% in anhydrousmethanol or in excess of that present in the aze'otropes 94% alcohol and91% isopropyl alcohol. Greater orlesser amounts of water than as statedmay be used; however, best results are obtained with the use of addedamounts of water within the percentage range stated. For convenienceherein I term these alcoholic solvents "aqueous alcohol mixtures."

Another class of diluent solvents in accordance with the present inention comprises mixtures of an. azeoti'opic concentrated alcoholsolvent with a non-solvent and water. Examples of such dilnents aremixtures of 95% ethyl alcohol or 91% isopropyl alcohol withdichlorethylene, trichlorethylene, ethyl acetate, benzene, cyclohexane,etc. and water. In this class of diluent solvents I also includencn-aqueous azeotropic mixtures of anhydrous methyl alcohol with hexane.cyclohexane. benzene, carbon tetrachloride. dichlorethylene.trichloretliylcne, acetone, methyl acetate, ethylacetate. methyl ethyllretone, etc, because one constituent of the mixture, methyl alcohol. isa zein solvent.

In addition to the foregoing, wherein at least one constituent of a.diluent solvent mixture is a aein solvent. the diluent solvents may besuitable azeotropic mixtures which are zein protein solvents wherein theindividual constituents of the mixture are non-solvents for zeinproteins. Thus, they may be azeotropic mixtures of water on the one handand dioxan or butyl alcohol on the other. Dioxan forms with water aconstant bolling point mixture containing 80% dioxan boiling at 86.9 C.;and butyl alcohol forms with water a constant boiling point mixturecontaining 63% butyl alcohol boiling at 92 C. They may also be suitableaqueous azeotropic mixtures which "are non-solvents for Zein proteinssuch as ethyl methyl ketone and water. And they may also be non-aqueousazeotropic mixtures of anhydrous ethyl alcohol or anhydrous isopropylalcohol with hexane, cyclohexane, benzene, carbon tetrachloride,dichlorethylene, trichlorethylene, acetone, methyl. acetate, ethylacetate, methyl ethyl ketone, etc.

The diluents may also be suitable non-solvents of low polaritycharacterized by the presence of -O, Cl, NH2, COOH groups, etc. Examplesof such diluents are dioxan, dichlorpentane, ethylene dichloride,dichlorethyl ether, etc. They may also be miscible hydrocarbons such asbenzene, hydrogenated naphtha, etc. Or they may be suitable non-solventsof high polarity such as anhydrous ethanol, anhydrous isopropanol orwater.

Zein solutions of a desired concentration and of a wide applicabilitycan be obtained directly from gluten by having in the final solution asthe only solvent or as the main solvent for zein, a relatively highboiling point solvent having the required balance of polar and non-polarradicals as described herein. It is now well established that theviscosity, gelling tendencies, and prac tlcal usability of zeinsolutions are in no small part dependent upon the character of thesolvent in which the zein is dissolved.

Zein or zein-containing extract solutions containing any one or more ofthe foregoing base solvents, in accordance with the present invention,may be boiled, distilled or otherwise treated to remove part or all ofthe diluent. It is evident that practically all of the diluent,including any water carried from the gluten to the extract solution, maybe removed, thereby obtaining solutions of zein or zein-containingproteins, in the base solvent which, for all practical purposes, aresubstantially anhydrous. Such solutionsvary widely in character,depending upon the choice of solvents or solvent mixtures used, as is tobe expected, and some of them may undergo changes (apparentinsolubility, for example). during the diluent and water removal whichaffect the solvent characteristics of the zein and zein-containingproteins in the base solvent utilized. These changes, where they takeplace, are not of a permanent character and it is possible to effect are-solu'tion of the zein or zein-containing proteins in the basesolvents by the addition of a small amount of water, say in the order offrom about 1 to 3% by weight, or an equivalent amount of other highlyhydroxylated compound, such as methyl or ethyl alcohol or a mixture ofsuch compounds.

In the preparation of useable solutions having a wide field ofapplicability. I prefer that the removal of diluent and water becontrolled so as to leave in the final solutions at least about 1 to 3%by weight of water or an equivalent amount 'of other highly hydroxylatedcompound. preferably water. Where this is not possible. water may beadded to the final solution, in the amounts stated. While water is, ingeneral, not

an essential constituent of some of the solutions formed in accordancewith the present invention, the solutions are generally of an improvedcharacter when they contain small amounts of water. The solutions maycontain larger amounts of water, say between 5 to 10%, or even more.

It is manifest that the nature and properties of the finished solutionwill be determined by the nature of the base solvent, the amount of zeinprotein present in the solution and the type or character of the zeinprotein extracted by the particular diluent used. It is apparent thatwith the solvent and diluent combinations possible, a wide variety ofsolutions for many uses can be produced by the methods of the presentinvention.

Within the range of the many possible combinationsand the methods inaccordance with the present invention, solutions may be produced whichrequire further adjustment or modification in order to secure improvedsolution or desired stability and controlled gelling properties. Suchadjustments or modifications can be readily effected by the use ofrosin, fatty acids, compatible amines such as monoethanolamine,triethanolamine, etc., amine soaps oi! rosin or fatty acids, or by thevarious methods and materials for producing stable, controlled gelling,zein solutions described in my issued Patents Nos. 2,185,122. 2,246,779and 2,298,548. The addition of suitable materials for effecting desiredmodification or adjustment may be made to the extract solution beforedistilling off the diluent or to the final solution. The preferableprocedure and materials with particular solutions may be readilydetermined by experimentation.

In the following examples I disclose illustrative methods for producingzein or zein-containing solutions directly from gluten in accordancewith the present invention. In the examples and elsewhere throughout thespecification, the term "parts indicates parts by weight.

Example 1.A solvent mixture containing 72 parts of anhydrous isopropylalcohol (99%), 40 parts of diethylene glycol and 8 parts of ethyleneglycol was added to 30 parts of powdered gluten in a vessel. The mixturewas heated to about F. and held at about that temperature for about hourwith stirring to extract the zeincontaining proteins from the gluten.The mixture was then forced through a filter to separate thezein-containing extract and the extract was then slowly heated to about250 F. and held at about that temperature with stirring until cessationof visible boiling. The residue was a solution of zein-containingproteins principally in the mixture of glycols.

Example 2.-A solvent mixture containing 72 parts of anhydrous denaturedalcoholU'Paco), 40 parts of diethylene glycol and 8 parts of ethyleneglycol was added to 30 parts of powdered gluten. The procedure was as inExample 1 and the resulting residue was a solution 01' zeincontainingproteins principally in the mixture of glycols.

At the cessation of boiling as referred to in the examples someproportion of the lower boiling, constituents of the diluent originallyused remains in the final solution. The proportion thereof so remainingdepends upon the final temperature and the boiling point curve of themix ture. Considerable proportions of the diluent or of itsconstituents, including water, may remain without causing gelling of thefinal solution inreasonable periods of time. This is particularly truewhere the glycols are used. In this respect the final solutions showdifferences from solutions of commercial rein containing large amountsof water as in the prior art, apparently by reason of some changes inthe character or structure of the zein-containing proteins of the corngluten taking place in the process of the present invention. the natureof which changes is not as yet understood.

In general and influenced by the type and amount of zein proteinpresent, the solutions prepared as described above and the coatingcompositions prepared therefrom have the properties, particularly whenheated, of being able to give up their solvent or solvents readily, andwhen applied to any surface they quickly and readily form tough,flexible, non-tacky, hard and enerally transparent coatings even whenretaining some solvent. The coatings formed by these zein-containingsolutions and coating compositions are very strong and have adherentproperties. In these solutions and coating compositions the film formingproperties thereof can be built up to produce films of great toughness,flexibility. hardness and gloss. Under normal temperature conditions.many of the zein-containing solutions or coating compositions willproduce non-blushing coatings on drying, without the aid ofsupplementary anti-blushing agents as in the prior art.

The coating compositions prepared from the above solutions may bemodified and used as fullydescribed in the aforementioned applicationSerial No. 467.402.

While my invention has been described in connection with certainspecific examples, it is, of

course, obvious it is not to be construed as limited to these examplesor to the details of the methods set forth therein, since obviouschanges in materials, proportions and method details will be apparentfrom the foregoing.

In the claims, the expression an elevated temperature in the order ofabout 120 F. to about 170 F. is not to be construed as a precisecritical range, but, rather, as' a range of temperatures indicative ofthe elevated temperature at which the extractions may be carried out.

I claim:

1. The method of preparing directly from gluten 3. solution ofzein-containing proteins in a solvent or mixture of solvents comprisingas an essential solvent constituent for the zein-containing proteins. asolvent having a boiling point above about 125 C. and having aproportion of polar to non-polar radicals which lies within a rangeextending between the limits of the proportion of polar to non-polarradicals of methanol and the proportion of polar to non-polar radicalsof ethanol, whichcomprises contacting gluten with a solvent mixture atan elevated temperature in the order of about 120 F. to about 170 F. toextract zein-containin proteins from the gluten, said solvent mixturecomprising the aforesaid zein-containing protein solvent having aboiling point above about 125 C. and a miscible diluent therefor havinga boiling point below about 125 C. which is a non-solvent for zein,separating the extract from the residual gluten and removing at leastpart of the diluent from the extract to form the aforesaid solution.

2. The method of preparing directly from gluten 2. solution ofzein-containing proteins in a solvent or mixture of-solvents comprisingas an essential solvent constituent for the zein-containing proteins, asolvent having a boiling point above about 150 C. and havin a proportionof polar to non-polar radicals which lies within a range extendingbetween the limits of the proportion of polar to non-polar radicals ofmethanol and the proportion of polar to non-polar radicals of ethanol.which comprises contacting gluten with a solvent mixture at an elevatedtemperature in the order of about F. to about 170 F. to extractzein-containing proteins from the gluten, said solvent mixturecomprising the afdresaid zein-containing protein solvent having aboiling point above about 150 C. and a miscible diluent therefor havinga boiling point below about C. which is a non-solvent for zein,separating the extract from the residual gluten and removingsubstantially all of the diluent from the extract to form the aforesaidsolution.

3. The method of preparing directly from gluten a solution ofzein-containin proteins in a solvent or mixture of solvents comprisingas an essential solvent constituent for the zein-containing proteins, asolvent having a boiling point above about C. and having a proportion ofpolar to non-polar radicals which lies within a. range extending betweenthe limits of the proportion of polar to non-polar radicals of methanoland the proportion of polar to non-polar radicals of ethanol, whichcomprises contacting gluten with a solvent mixture at an elevatedtemperature in the order of about 120 F. to about F. to extractzein-containing proteins from the gluten, said solvent mixturecomprising the aforesaid zein-containing protein solvent having aboiling point above about 150 C. and a miscible diluent therefor havinga boiling point below about 125 C. which is a non-solvent for zein,separatin the extract from the residual gluten and removing at leastpart of the diluent from the extract to form the aforesaid solution.

4. The method of preparing directly from gluten a solution ofzcin-containing proteins in a solvent or mixture of solvents comprisingas an essential solvent constituent for the zein-containing proteins, asolvent having a boiling point above about 150 C. and having aproportion of polar to non-polar radicals which lies within a rangeextending between the limits of the proportion of polar to non-polarradicals of methanol and the proportion of polar to non-polar radicalsof ethanol, which comprises contacting gluten with a solvent mixture atan elevated temperature in the order of about 120 F. to about 170 F. toextract zein-containing proteins from the gluten, said solvent mixturecomprising the aforesaid zein-containing protein solvent having aboiling point above about 150 C. and an anhydrous miscible diluenttherefor having a boiling point below about 125 C. which is anon-solvent for zein, separating the extract from the residual glutenand removing at least part of the diluent from the extract to form theaforesaid solution.

5. The method of preparing directly from gluten a solution ofzein-containing proteins in a mixture of solvents comprising diethyleneglycol and ethylene glycol as essential solvent constituents for thezein-containing proteins, which comprises contacting gluten with asolvent mixture at an elevated temperature in the order of about 120 F.to about 170 F. to extract zeincontaining proteins from the gluten, saidsolvent mixture comprising diethylene glycol, ethylene glycol andanhydrous isopropyl alcohol, separating the extract from the residualgluten and removing at least part of the isopropyl alcohol from theextract to form the aforesaid solution.

6. The method of preparing directly from gluten a. solution ofzein-containing proteins in a mixture of solvents comprising diethyleneglycol and ethylene glycol as essential solvent constituents for thezein-containing proteins, which comprises contacting gluten with asolvent mixture at an elevated temperatur in the order of about 120 F.to about 170 F. to extract zeincontaining proteins from the gluten, saidsolvent mixture comprising diethylene glycol, ethylene glycol andanhydrous ethyl alcohol, separating the extract from the residual glutenand removing at least part of the diluent from the extract to form theaforesaid solution.

ROY E COLEMAN.

